Auralization of Urban Environments: Benchmark and Evaluation

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With the research project, we want to create a broader fundament towards the auralization of urban environments. The challenge to auralize virtual acoustic environments imposes high demands on methodology and implementation of both propagation simulation and digital signal processing. In particular, urban scenarios push the efforts to the limits, as many fast-moving sound sources present in a built environment, where sound is repeatedly reflected and diffracted. As an outcome of the completed research project on real-time diffraction modeling, a fast propagation path finding algorithm has been established that is able to integrate both reflections and diffractions. Real-time rates are met by using advanced delay lines, short filter units and a new binaural direction clustering algorithm that generates a binaural auralization audio stream at quasi-constant load. A significant discrepancy between theoretically possible propagation paths and the actually processable path number on a state-of-the-art computer has been identified. The assumption is made, that the vast majority of theoretical propagation paths becomes imperceivably due to both the fact that a) sound is coming from many incident directions and b) many different sound sources are present. To solve this issue, an evaluation regarding the importance of paths must be conducted. It is planned to investigate the importance of propagation path on a technical and perceptual level. The technical approach is based on comparison of results from acoustic scale model measurements and from simulations. The benchmark cases represent typical situations with buildings and street canyons in urban environments. Variations in the modeling are to be compared with the actual transfer functions to reveal the consequence on sound pressure level and interference pattern, e.g. for higher reflection and diffraction orders. Finally, in a listening experiment, perceptual influences are investigated when different importance filters are applied to the set of theoretical propagation paths. The specification of level thresholds and audibility of coloration effects in this context are studied by ABX comparison. The main result of the proposed project is an open benchmark for urban situations as reference with high quality supporting material and documentation (which is not available at the moment) and a catalogue of recommendations how to filter theoretical propagation paths based on perceptual importance for different contexts, e.g. to run an outdoor auralization on a consumer desktop PC.